In the spring of 1847 Reed toured Europe to gather information on institutions serving the purpose, and in October the project to found the Asylum began. Lord Palmerston, Baron Rothschild and Lord Ashley became officers of the charity.

In 1848 a building was purchased and the first patients admitted. This building, Park House at Highgate, quickly proved to be too small and a new building was commissioned. Several designs were submitted in competition and a Mr. Moffat's was chosen. The builder was John Jay of London Wall, whose varied work included substantial railway construction contracts, rebuilding the Houses of Parliament after the 1833 fire, and smaller architect-designed projects such as the Abney Park Chapel and Trinity Independent Chapel. The building was entirely financed by public subscription and Queen Victoria subscribed 250 guineas in the name of Edward Prince of Wales, who became a life member. Prince Albert took a special interest from the beginning. He laid the foundation stone in June 1853 and opened the Asylum in June 1855. In 1862 Queen Victoria conferred a Royal Charter on the asylum.

John Langdon Down (after whom Down syndrome was named) was medical superintendent of the hospital from 1855 to 1868. At this time patients slept in fifteen-bed dormitories and there was one member of staff to each seven patients. Tuberculosis accounted for the majority of deaths in the institution.[2]

Patients were taught manual trades such as carpentry, printing and brush-making, as well as domestic, garden and farm duties.

The hospital closed in 1997, as part of the Government's long-term plan to transfer the care of people with learning disabilities into the community, and was converted into apartments: the development is called Royal Earlswood Park.